This invention relates to frequency adjusting methods and systems for adjusting the frequency of an electrical signal to approximate to a desired frequency.
Synthesis of a desired frequency can be carried out using a phase-locked loop to generate an output frequency which is a whole multiple of a base frequency fed to the phase comparator of the loop, the multiplication factor being introduced by an integer division operation applied to the output frequency feedback. A change in output frequency to approximate that frequency to a desired value is effected by changing the multiplication factor of the loop. Clearly the output frequency can only be adjusted in steps equal to the base frequency. Since it is undesirable to have a very low base frequency or a very high multiplication factor, frequency synthesis so effected either has large steps in output frequency or is restricted to low frequency bands.
An object of the invention is to provide improved frequency adjusting or synthesising methods and systems.